The phrase "chance on" is often used to describe an unexpected encounter or discovery. However, there are several other synonyms that can be used in its place. Some examples include stumble upon, happen upon, come across, encounter, find, and discover. Each of these words conveys the same idea of something being stumbled across or found unexpectedly. "Stumble upon" and "happen upon" both add an element of surprise to the discovery, while "come across" and "encounter" suggest a more deliberate effort to find something. "Find" and "discover" are more general terms that can be used to describe any type of unexpected discovery.